There's something I don't understand. When Feynman starts to talk about why light is reflected such that the angle of incidence equals the angle of reflection, he gives an example where the light source is the same distance from the mirror as the photomultiplier (for simplicity). This gives the final result of the probability amplitude. This is mostly due to the middle part of the mirror, when the angles of the probability "vectors" differ so slightly that they add up greatly, where as later they matter less and less to the final vector.

This is important for every explanation (that I have thus far) in the book. The fastest path for the photon is the most likely.

By taking certain parts away from the mirror, he demonstrated that what was going on really was reflection. I understood this.

However, when I was thinking about this later, I tried to think of a scenario where the photomultiplier is further or closer to the mirror than the light source. It came to my attention that the fastest path that a photon could take would

*not*be such that the angle of incidence were to equal the angle of reflection, but such that the length of the line from the light source to the mirror would equal the length of the line from the photomultiplier to the mirror. When the photomultiplier and the light source are at the same distance from the mirror, then those lines are such that the angle of incidence were to equal the angle of reflection, as in the book.

However, light should always travel such that the angle of incidence were to equal the angle of reflection. There's something I'm not grasping here.

Thanks